Collection Expressions in C# 12.0

C# 12.0 introduces a new feature known as collection expressions, which aims to simplify the syntax for creating and initializing collections. This feature is part of the ongoing evolution of the C# language, providing developers with more concise and readable code.


Collection expressions offer a new, terse syntax for creating common collection types without the need for verbose initialization patterns previously required in C#. The syntax [e1, e2, e3, ...] allows for the direct creation of arrays, lists, and other collection types.

Syntax and Usage

The basic syntax for a collection expression is as follows:

var numbers = [1, 2, 3, 4, 5]; // Creates an int array

This expression creates an array of integers. The type of the collection is inferred from the context, eliminating the need for explicit type declarations in many cases.

Spread Operator

A significant addition to the syntax is the spread operator .., which allows for the inclusion of other collections within a new collection expression:

var moreNumbers = [0, ..numbers, 6]; // Spreads 'numbers' between 0 and 6

Here, moreNumbers will be an array containing [0, 1, 2, 3, 4, 5, 6].

Supported Types

Collection expressions can be used to create several collection-like types, including:

  • Array types: Such as int[].
  • **Span and ReadOnlySpan**: Useful for memory-efficient collections.
  • Types with collection initializers: Like List<T>, where the type T can be inferred.


The advantages of using collection expressions are manifold:

  • Conciseness: Reduces the boilerplate code required to instantiate collections.
  • Readability: Makes the code more intuitive and easier to understand at a glance.
  • Performance: Avoids multiple reallocations of memory that can occur with collection initializers due to the use of .Add invocations without an initial capacity.


Collection expressions in C# 12.0 represent a significant step forward in the language’s design, offering developers a more streamlined and efficient way to work with collections.

Thank you for reading.

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